Method of forming antistatic film and image display device formed thereby

ABSTRACT

The invention provides a method of forming an antistatic film with even thickness and at high speed even in a substrate having micro depressions and projections in its surface. A fine particle dispersion solution is prepared by adding a solution which decreases the absolute value of a ξ potential at the fine particles and a solution which decreases dispersion stability of the fine particles into a solution in which metal oxide fine particles are stably dispersed, a substrate having an insulating surface is immersed in the fine particle dispersion solution to deposit a fine particle aggregation film, and then an antistatic film is obtained by performing heat treatment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of immersing a substrate in afine particle dispersion solution, depositing a fine particle film on asurface of the substrate, and forming an antistatic film. Particularlythe invention relates to the film depositing method suitable for formingthe antistatic film on the substrate whose surface has micro depressionsand projections, and an image display device and a television devicewhich are formed thereby.

2. Related Background Art

In the method of depositing various kinds of functional films on thesubstrate, vacuum evaporation, sputtering, a CVD method, and the likeare widely known as the method of depositing the film from a gas phase.Spray coating, a dipping and pulling-up method, spin coating,electrolytic plating, electroless plating, colloidal electrodeposition,a sol-gel method, liquid-phase deposition, and the like are well knownas the method of depositing the film from a liquid phase. These filmdepositing methods are appropriately used depending on characteristicsof each method.

In the vacuum evaporation and the sputtering which are of the method ofdepositing the film from the gas phase, although film characteristicscan be precisely controlled, directional properties exist in depositingthe film. Therefore, although the vacuum evaporation and the sputteringare suitable for the film deposition on the plane-shaped substrate, itis difficult to deposit the film on the whole surface of the substratein which the surface is not smooth. Throughput is also low because avacuum film depositing apparatus is required. When the film is upsized,there is a problem that the apparatus becomes very expensive.

In the atmospheric pressure CVD method, although a vacuum installationis not required, generally it is necessary to heat the substrate onwhich the film is deposited to a high temperature, and it is necessarythat the substrate has high heat-resisting properties. Because atemperature distribution of the substrate is reflected to acharacteristic distribution of the film, the even temperaturedistribution is required in depositing the film, and the temperaturedistribution is difficult to control particularly in the substratehaving a complicated shape.

Generally the gas phase film depositing method is suitable forproduction of a thin film because a film material is supplied as gas.However, because material density is low, there is the common problemthat film deposition speed is relative low. On the other hand, theliquid phase film depositing method has advantages that solute densitycan be largely increased and the film deposition speed is large, and thethroughput is high, when compared with the gas phase film depositingmethod. Therefore, the liquid phase film depositing method is widelyused in fields in which cost reduction is required.

In the electrolytic plating and the electroless plating, the filmdeposition speed is high, the film can be deposited over the substrateat once at a low temperature, and the film deposition can be performedat low cost. However, in the electrolytic plating and the electrolessplating, the film material is limited to a metal material in whichoxidation and reduction are easy to occur.

In the electrodeposition, because pigment fine particles in colloidaldispersion are attracted to the substrate Coulomb attraction in anelectrophoresis phenomenon, it is necessary that the substrate itself isconductive.

In the dipping and pulling-up method, the spin coating, and the spraycoating, the film can be deposited on the substrate having a large areawith an extremely simple apparatus, and these methods are the low-costfilm depositing means used in various fields. A sol-gel solution, a fineparticle dispersion solution, and the like can be used as the filmmaterial, and a degree of freedom is large in selecting the substratematerial and the film material. However, surface tension has a largeinfluence on these film-depositing methods when a solution layer formedon the surface of the substrate is dried, so that it is difficult thatthe film is evenly deposited on the substrate having a micro,complicated shape. As shown in FIG. 9A, when the film is deposited onthe surface of a substrate 5 having micro depressions and projections bythese methods, as shown in FIG. 9B, the solution containing the filmmaterial is attracted to the depressions on the surface of the substrateby the surface tension, and it is inevitable that films 41 are thick inthe depressions and films 42 are extremely thin in the projections. Asshown in a partially enlarged view of FIG. 9C, ideally it is desirablethat the film has the even thickness in both the depressions and theprojections. However, currently the film shown in FIG. 9C is notrealized.

In the liquid phase deposition (LPD), a technology in which an oxidethin film is mainly grown on the surface of the substrate by utilizing asolution chemical reaction between film raw materials solved in thesolution is actively developed in recent years, and Japanese PatentApplication Laid-Open No. H06-116424 discloses the technology. In thetechnology, the film can be deposited across the surface at a relativelylow temperature irrespective of the shape of the substrate. Thetechnology is promising in the future. However, currently a filmdeposition time is long and the available substrates and film materialsare restricted.

On the other hand, a phenomenon in which the fine particles are absorbedto the surface of the substrate in the solution depending on conditionsis well known, and the technology which prevents the absorption offoreign materials is widely researched particularly in the field of awashing technology (see Japanese Patent Application Laid-Open Nos.H03-74845 and H09-22885).

However, the absorption of the foreign material becomes only a state inwhich the surface of the substrate is sparsely contaminated by theextremely small amount of foreign material, and the absorption of theforeign material can not positively be utilized as means for forming thefunctional film on the substrate.

The technology, in which the thick and even fine particle film isdeposited on the whole area of the insulating substrate surface havingthe micro depressions and projections at high speed by the simpletechnique as shown in FIG. 9C, is not developed in the conventionaltechnology described above.

A plane type of display device which utilizes electric fieldelectron-emission (FED) can be cited as an example of a member whichneeds the above-described technology.

In the plane type of display device (FED), it is necessary to provide awithstanding atmospheric pressure support body (spacer) because theinside is in a vacuum. In the spacer, it is necessary that an evenantistatic film is formed on the whole insulating substrate so that thespacer withstands high voltage and electric charges are not accumulatedon the surface by electron collision (see Japanese Patent ApplicationLaid-Open No. 2000-311605 (U.S. Pat. No. 6,485,345) and No. 2000-311609(U.S. Pat. No. 6,600,263). In addition, in order to restrain theemission of secondary elections on the spacer surface, it has recentlybeen studied to manufacture the spacer by forming an antistatic film ona substrate having micro depressions and projections on its surface (seeJapanese Patent Application Laid-Open No. 2003-223858(US-2003-141803A)). Therefore, the above-described film depositingmethods are studied for the means for forming the antistatic film.

A problem of the invention is to realize the even resistant filmdeposition on the insulating substrate surface having the microdepressions and projections at high speed and at low cost, which isdifficult to realize by the conventional gas phase film depositiontechnology and liquid phase film deposition technology, particularly thedipping and pulling-up method, the spin coating, and the spray coating.Mainly the film depositing method of the invention enables theantistatic film to be formed on the withstanding atmospheric pressuresupport body (spacer) having the micro depressions and projections,which is used for the plane type of display device.

SUMMARY OF THE INVENTION

In a primary aspect, the present invention is directed to a method offorming a resistance film on a surface of a substrate having aninsulating surface, the resistance film having a sheet resistivity lessthan of the insulating surface. This method of forming the resistancefilm comprises the steps of immersing the substrate in a solution inwhich fine particles made of a material of the resistance film aredispersed to wet a fine particle dispersion solution to the surface ofthe substrate, decreasing an absolute value of a ξ potential at the fineparticles in the fine particle dispersion solution wetted to the surfaceof the substrate so as to make it smaller than an absolute value of ξpotential at the fine particles when these particles are being dispersedin the solution, to deposit a fine particle aggregation film on thesurface of the substrate, and burning the fine particle aggregation filmto form the resistance film.

Preferably, in the depositing step, the absolute value of the ξpotential at the fine particles in the fine particle dispersion solutionwetted to the surface of the substrate is set in the range of 0 to 40mV.

It is preferable that the solution in which the fine particles made ofthe resistance film material are dispersed is a solution obtained byadding a diluting solution (B) having a polarity smaller than that ofwater and an adjusting solution (C) reducing the dispersion stability ofthe fine particles into an aqueous solution (A) in which the fineparticles made of the resistance film material are dispersed.

It is preferable that the depositing step includes a step of adding anaggregation solution (E) having a polarity smaller than that of thewater and the dielectric constant lower than that of the water into thesolution wetted to the surface of the substrate, the fine particlesbeing dispersed in the solution.

It is preferable that the depositing step includes a step of immersingthe substrate immersed in the solution in which the fine particles aredispersed into an aggregation solution (E) having a polarity smallerthan that of the water and a dielectric constant lower than that of thewater.

It is more preferable that the polarity of the aggregation solution (E)is equal to or smaller than that of the diluting solution (B).

It is more preferable that a cycle of the wetting step and thedepositing step is repeated plural times.

It is preferable that there is further comprised a step of immersing thesubstrate into a re-dispersion solution (F) after the depositing step,the re-dispersion solution having a polarity larger than that of theaggregation solution (E) and a dielectric constant higher than that ofthe aggregation solution.

In another aspect, the present invention is also an image display devicecomprising a rear surface plate which has electron-emission elements, afront surface plate which has an image display member, and anatmospheric pressure-resistant support body which is located between therear surface plate and the front surface plate, wherein the atmosphericpressure resistant support body has a substrate and an resistance filmwith which the substrate is covered, and the resistance film is formedby any one of the above-described methods.

In further another aspect, the present invention is also a televisiondevice comprising the above-described image display device, a televisionsignal receiving circuit, and an interface unit which connects the imagedisplay device and the television signal receiving circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C and 1D are a view schematically showing a process of afirst embodiment of the invention;

FIGS. 2A, 2B, 2C, 2D and 2E are a view schematically showing the processof a second embodiment of the invention;

FIGS. 3A, 3B and 3C are an explanatory view showing a basic principle ofthe invention;

FIGS. 4A, 4B and 4C are an explanatory view showing the basic principleof the invention;

FIGS. 5A, 5B and 5C are an explanatory view showing the basic principleof the invention;

FIGS. 6A, 6B, 6C, 6D and 6E are a view schematically showing the processof a fifth embodiment of the invention;

FIGS. 7A, 7B and 7C are a view schematically showing the process of asixth embodiment of the invention;

FIG. 8 is a view schematically showing a structure of a plane type ofimage display device for which a support body, to which the invention isapplied, is use; and

FIGS. 9A, 9B and 9C are a schematic view showing a state in which anantistatic film according to the invention is formed on a substratesurface having micro depressions and projections; and

FIG. 10 is a block diagram of a television device of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Since the film depositing method of the invention is not affected bysurface tension because the film is formed in a solution, and theantistatic film having the even thickness can be formed on the substratesurface having the micro depressions and projections. Since the filmdepositing method of the invention includes the simple method ofimmersing the substrate in the solution, the complicated and expensiveapparatus is not required, and the film depositing method of theinvention can respond easily to upsizing of the substrate and massproduction. Further, in the film depositing method of the invention, thesolution used in the process is high in a utilization ratio, and theantistatic film can efficiently be formed at high film deposition speed.

According to the invention, the antistatic film having the eventhickness can be formed on the surface of the member having the microdepressions and projections, such as the surface of the withstandingatmospheric pressure support body, in the plane type of image displaydevice, so that cost reduction can be achieved in the production whilereliability of the device can be improved.

Generally, in the fine particles being dispersed in the solution, anelectrical double layer is formed in the surface, and the electricaldouble layer has a positive or negative electrical charge. An outer hullwhich is moved with particles is referred to as slide plane in theelectrical double layer formed on the surface. In a potentialdistribution, the slide plane is usually referred to as a ξ potential,and the ξ potential is one which can be measured from the outside. It iswell known that the ξ potential is largely changed depending on a typeof fine particle surface material, a species of solvent, electrolyteconcentration, hydrogen ion concentration (pH), a surface active agent,and the like.

FIGS. 3A, 3B and 3C to FIGS. 5A, 5B and 5C are a view schematicallyshowing a reaction of dispersion and aggregation of the fine particles.

When the fine particles in the solution are holed at the dispersionstate as shown in FIG. 3A, the attraction 52 between molecules whichattenuates in inverse proportion to the fifth to seventh powers of thedistance between the fine particles and the Coulomb repulsion 53 whichattenuates in inverse proportion to the first and second powers of thedistance between the fine particles are exerted between the fineparticles 51. In addition, the composite force 54 obtained by addingtogether the attraction 52 and the Coulomb repulsion 53 is denoted witha solid line. These different two forces are largely different inarrival distance (distance which a force reaches) from each other;therefore if there are surface charges larger than a certain degree, theCoulomb repulsion between the fine particles which becomes predominantprevent the fine particles from coming near to each other. This Coulombrepulsion, which is due to the charges on the fine particle surface, isgenerally measured as a ξ potential.

FIG. 3B shows a situation in which the fine particles are aggregated bythe attraction between molecules because the Coulomb repulsion isweakened due to the decreased surface charges of the fine particles.Thus, the aggregation of the fine particles is explained by the declineof the Coulomb repulsion caused by the charges on the particle surface,and the surface charges do not necessarily become zero.

FIG. 3C shows a situation in which the aggregation of the fine particlesprogresses in the above-described manner and as a result the Coulombrepulsion is re-created. The re-created Coulomb repulsion results fromthat the attraction between molecules, (which reaches as far as a shortdistance) attenuates in inverse proportion to the fifth to seventhpowers of the distance and the Coulomb force (which reaches as far as along distance) attenuates in inverse proportion to the first and secondpowers of the distance.

That is, since the attraction between molecules reaches only thesurfaces of the closest particles, even if the aggregation of the fineparticles progresses to become a cluster of fine particles, theattraction between molecules are not added together. By contrast, sincethe Coulomb repulsion reaches as far as a long distance, the residualcharges of the particles located in the back of the aggregation body areadded together for action. Therefore, the aggregation of the fineparticles progresses and as the size of the aggregation body increases,the potential barrier of the Coulomb repulsion is again formed, and haveoccurs the phenomenon that new fine particles are again prevented fromcoming near to each other.

FIGS. 4A, 4B and 4C are view schematically showing the condition ofdispersion and aggregation of the fine particles in the solution and onthe substrate surface.

FIG. 4A shows the condition in which the dispersion of the fineparticles is stably maintained, and the fine particles are aggregatedbecause both the surface of the particle 61 and the surface of thesubstrate hold sufficient surface charges.

FIG. 4B shows the condition of aggregation of the fine particles and thecondition of forming the film onto the substrate in the case that thedecrease of the absolute of the ξ potential is small, that is, theresidual charges are large. Since the residual charges on the fineparticle are comparatively large, the Coulomb repulsion again becomespredominant with a cluster of a few particles; therefore the size of theaggregation particle 63 is small and the thickness of aggregation film64 formed on the substrate is also decreased.

FIG. 4C shows the condition of aggregation of the fine particles and thecondition of forming the film onto the substrate in the case that thedecrease of the absolute of the ξ potential is large. Because of thesmall residual charges on the particle surface, the Coulomb repulsiondoes not become predominant unless the particles are largely aggregated;therefore the size of the aggregation particle 65 is large and thethickness of the aggregation film 66 formed on the substrate isincreased.

FIGS. 5A, 5B and 5C show that the aggregation film formed on thesubstrate surface has a constant thickness and a smooth surfaceproperty, which is the uniqueness of the present invention. Where, theterm “smooth” means following a shape of the substrate surface.Specifically, if the substrate has a surface shape of depressions andprojections, the “smooth” means that a film of depressions andprojections is formed following the surface shape of the substrate.

FIGS. 5A, 5B and 5C are an explanatory view in the case that thedepositing step is repeated plurality times.

As shown in FIG. 5A, when the aggregation film formed on the substratesurface by the initial aggregation reaction has an uneven filmthickness, including a thin film part 71 and a thick film part 72, therepeat of the same aggregation reaction as shown in FIG. 5B causes newaggregation of the fine particles to be restrained at the thick filmpart 72 because the large Coulomb repulsion already occurs as a totalsum of the cluster of particles at this part 72. While, at the thin filmpart 71, the aggregation reaction progresses at the thin film part 71because the attraction between molecules becomes predominant because ofthe small Coulomb repulsion as the total sum is small.

Though such a process, the aggregation film 75, which is rendered smoothby the balancing action of the attraction and repulsion of the particlesthemselves, is formed, as shown in FIG. 5C. In short, one of uniquefeatures of the present invention resides in being able to control thethickness of the film by the control of the ξ potential of the fineparticle.

The present invention is to mainly utilize the actions as stated above.

However, behavior of the dispersion and aggregation of the fineparticles is a very complex phenomenon, and it is finally determined byan interaction between the electrical double layers formed near thesurface of the solid in the solution. An abundance ratio of water, amolecular structure (polarity and dielectric constant) of the organicsolvent, characteristics of a surface active agent and the like can becited as an example which has an influence on the structure of theelectrical double layer. It is known that aggregation speed and thethickness of the fine particle absorption layer are varied by thechanges in the above-described factors. These are the extremelycomplicated phenomenon, and currently it is difficult to theoreticallycompletely explain the phenomenon.

Through trial and error of various additives, species of solvents,procedures, and immersion techniques, the invention enables the evenfine particle film to be formed on the surface of the substrate at highspeed by the simple method of immersing the substrate in the fineparticle dispersion solution.

The film depositing method of the invention comprises the steps of thesteps of immersing the substrate in a solution in which fine particlesmade of an antistatic film material are dispersed to wet a fine particledispersion solution to the surface of the substrate, decreasing anabsolute value of a ξ potential at the fine particles in the fineparticle dispersion solution wetted to the surface of the substrate todeposit a fine particle aggregation film on the surface of thesubstrate, and burning the fine particle aggregation film to form theantistatic film. The invention will specifically described referring topreferred embodiments of the film depositing method of the invention.

Each of the solutions as used in the present invention has the followingcharacteristics.

The fine particle solution (A) is a solution in which particles aredispersed in water or a mixture of the water and an organic solvent. Itis desirable that a diameter of this particle ranges from 4 nm to 20 nm,and it is experimentally recognized that the more the diameterincreases, the less the deposition property decreases.

And, as the fine particle, not only a particle made of a simplesubstance but also a particle which is surface-modified with a silanolgroup or carbon group is used.

The adjusting solution (C) is selected for the purpose of adjusting thedispersion stability of the fine particles.

In the present invention, it is required that the adjusting solution (C)is made of a material which has an adjusting action of reducing thedispersion stability of the fine particles and causing the aggregationreaction that is sensitive to slight decrease of hydrated water aroundthe fine particles. Some of the surface active agents have such anadjusting action, and while the present invention uses tetramethylammonium hydroxide or hydroxide chlorine(trimethyl-2-hydroxyethylammonium hydroxy oxide solution) as quaternaryammonium, other materials having the same adjusting action may be used.

The diluting solution (B) is a solution used to decrease the absolutevalue of the ξ potential of the fine particle. The diluting solution (B)serves to decrease the absolute of the ξ potential to the vicinity ofthe boundary at which the fine particles in the fine particle dispersionsolutions are maintained beforehand in dispersion state so that theaggregation reaction is swiftly created in the vicinity of the surfacepole of the substrate in the next processing step. This dilutingsolution (B) uses an organic solvent of single substance or mixturewhich has a polarity smaller than that of water. In the example, therecan be mainly used alcohols.

The aggregation solution (E) is a solution used to cause the fineparticles in the fine particle dispersion solution to lose the hydrationstability to instantaneously create the aggregation of fine particles.The aggregation solution (E) has an action of robbing the hydrated wateraround the fine particles by soluble property to water a characteristicthat the aggregation of fine particles is created after beingsubstituted for the water due to a fairly small polarity. The organicsolvent which has a polarity smaller than the water is used as thisaggregation solution as well as the diluting solution (B). And, it ispreferable that the aggregation solution (E) has a polarity smaller thanthat of the diluting solution (B). Concretely, as the aggregationsolution (E), the alcohols of single substance or mixture can be used aswell as the diluting solution (B).

The re-dispersion solution (F) is a solution which has a polarity largerthan the aggregation solution (E), thereby causing the ξ potential ofthe fine particle to again rise. A value of the polarity of there-dispersion solution is selected in such a manner that only the fineparticles at the thick part of the aggregation film of fine particlesformed on the substrate surface by immersing in the re-dispersionsolution (that is, a part at which the total sum of the Coulombrepulsion is large and hence a bonding force is comparatively small) ispreferentially re-dispersed. If the polarity of this solution is toolarge (the ξ potential of the fine particle is too high), most of theformed fine particle aggregation film is lost; therefore it is necessaryto adjust the polarity of the solution by properly mixing two kinds ormore solvents. For instance, it is easy to perform the adjustment byselecting the alcohols in accordance with the number of carbons and mixthe selected ones.

Alcohol is preferably used as the water-soluble organic solvent used inthe solutions (B), (E) and (F) in the first to sixth embodiments.Specifically, methyl alcohol, isopropyl alcohol (IPA), n-propanol, orthe like is solely used or at least the two alcohols described above areused according to the characteristics required for each solution used ineach embodiment. Ethers such as dioxane, amines such as monoethylamine,glycol ethers such as methyl Cellosolve, ketones such as acetone,carboxylic acids such as acetic acid, and esters such as Carbitolacetate can be used as the water-soluble organic solvent by appropriateselection in addition to alcohols.

First Embodiment

The processing steps of the first embodiment of the present inventionare schematically shown in FIGS. 1A to 1D. In FIGS. 1A to 1D, 1 refersto the fine particles solution (A), 2 the diluting solution (B), 3 theadjusting solution (C), 4 the particle dispersion solution obtained bymixing the fine particle solution (A), diluting solution (B) andadjusting solutions (C), 13 the aggregation solution (E), and 5 thesubstrate.

Metal oxide is preferably used as the antistatic film material used inthe invention. Particularly it is preferable that the antistatic filmmaterial mainly any one of contains tin oxide, zinc oxide, and titaniumoxide. The fine particle contains 0.1 to 10 mass-percent metal oxide. Itis also possible that 1 to 20 mass-percent antimony and the like aredoped in the fine particle. A diameter of the fine particle preferablyranges from 4 to 20 nm.

The diluting solution (B) is a solution used to decrease the absolutevalue of the ξ potential of the fine particles in the fine particlesolution (A). Preferably, as the diluting solution (B), a solution whichhas a polarity smaller than that of the solvent of the particle solution(A) and which mainly contains a water soluble organic solvent having alow dielectric constant. And, for example, a water is used as a solventof the fine particle solution (A).

The adjusting solution (C) is a solution for adjusting the dispersionstability of the fine particle, and there is used an aqueous solutionsuch as quaternary ammonium or preferably, tetramethyl ammoniumhydroxide.

In the embodiment, the diluting solution (B) 2 is first added to thefine particle solution (A) 1. At this point, the kind and the additiveamount of the solution (B) 2 are adjusted so that only the addition ofthe solution (B) 2 does not generate the aggregation.

Then, the fine particle dispersion solution 4 is adjusted by adding thesolution (C) 3 into the above-described fine particle dispersionsolution (see FIG. 1A).

The substance 5 is immersed into the fine particle dispersion solution(1) 4 and the solution is oscillated for several seconds to severalminutes to cause the surface of the substance 5 to be sufficientlywetted with the fine particle dispersion solution 4 (see FIG. 1B). Thesubstrate 5 used in the present invention has an insulating surface, andpreferably contains Si in its surface.

This embodiment is a method of using the solution (E) to reduce the usedamount of the particle solution (A) as little as possible, therebyincreasing a utilization rate of an antistatic film material to a limitto attain a high film deposition speed.

The aggregation solution (E) used in the embodiment is one which reducesthe absolute value of the ξ potential of the fine particles further thanthe diluting solution (B). The aggregation solution (E) is prepared sothat the fine particle aggregation occurs instantly when the fineparticle dispersion solution 4 is dropped in the aggregation solution(E). Specifically the solution which mainly contains the water-solubleorganic solvent having the polarity equal to or smaller than that of thesolution (B) and having the dielectric constant equal to or lower thanthat of the solution (B) is used, as the solution (E).

The substrate 5 is pulled up from the fine particle dispersion solution4 and the substrate 5 is rapidly immersed in the solution (E) 13 withoutdrying (see FIG. 1C). By the operation, the large amount of aggregationsolution (E) 13 is substituted for the small amount of fine particledispersion solution (1) 4 wetting the surface of the substrate 5 toinstantly eliminate the dispersion stability of the fine particles.Therefore, almost all of the fine particles attracted to the surface ofthe substrate 5 are absorbed and aggregated to the surface of thesubstrate 5 to form the fine particle aggregation film 8 with extremelyhigh efficiency. In the embodiment, since the diluting solution (B) 2 isadded to the fine particle dispersion solution 4, the film thickness ofthe fine particle aggregation film 8 formed at one time is thicker, i.e.the film deposition speed is faster than that of the second embodiment.

In this embodiment, because the mixture of the solutions is limited tothe extremely small amount of solution which is moved by adhering to thesurface of the substrate 5, the functions of the fine particledispersion solution 4 and the aggregation solution (E) 13 aremaintained. Therefore, it is not necessary to newly prepare the fineparticle dispersion solution (1) 4 and the aggregation solution (E) 13,and it is possible to repeatedly perform the immersion in an alternatingmanner using the same fine particle dispersion solution (1) 4 and thesame solution (E) 13. The fine particle aggregation film 8 is depositedto the predetermined thickness by repeating the cycle of the alternatingimmersion, and then the antistatic film 9 is obtained (FIG. 1D).

In the same embodiment, the extremely small amount of fine particledispersion solution can efficiently be used for the formation of thefine particle aggregation film 8 on the substrate surface. Further, thealternating immersion of the substrate into the fine particle dispersionsolution and the aggregation solution (E) preferentially generates thefine particle absorption in the next cycle in a part where the substratesurface is exposed while the fine particles do not adhere, so that theaction of making the film thickness even can be obtained and theantistatic film having the even thickness can be formed in a short time.

Second Embodiment

A fourth embodiment is one in which the processes of the firstembodiment is improved. The fourth embodiment is a technique of formingthe extremely thin and even antistatic film.

FIGS. 2A, 2B, 2C, 2D and 2E schematically show the process of the fourthembodiment. In FIGS. 2A to 2E, the numeral 14 designates a re-dispersionsolution (F), and the same member as FIGS. 1A to 1D is designated by thesame reference numeral.

The re-dispersion solution (F) used in this embodiment is one whichincreases the dispersion stability of the fine particles. The solutionwhich mainly contains the water-soluble organic solvent having thepolarity larger than that of the aggregation solution (E) is used as thesolution (F), or the composition of the water-soluble organic solvent isprepared so as to obtain the combination in which the solution (F) islarger than the aggregation solution (E) in the polarity, i.e. thesolution (F) is higher than the solution (E) in the dielectric constant.

FIGS. 2A, 2B, 2C, 2D and 2E show an example in which the fine particledispersion solution (1) and the solution (E). The example shown in FIGS.2A, 2B, 2C, 2D and 2E, will specifically be described below.

Similarly to the first embodiment, the fine particle dispersion solution4 is prepared with the fine particle solution (A) 1, the dilutingsolution (B) 2, and the adjusting solution (C) 3 (see FIG. 2A). Thesubstrate 5 is immersed in the fine particle dispersion solution (1) 4(see FIG. 2B), and then the substrate 5 is rapidly immersed in thesolution (E) 13 (see FIG. 2C). The substrate 5 on which the fineparticle aggregation film 8 is deposited is pulled up and immersed inthe solution (F) 14 without drying (FIG. 2D). At this point, a part ofthe fine particles in the fine particle aggregation film 8 which isabsorbed and aggregated onto the surface of the substrate 5 is dispersedinto the solution (F) 14 again to become a state in which a fineparticle aggregation film 8′ having the film thickness thinner than thatof the fine particle aggregation film 8 is left. The re-dispersion forceof the fine particles can be adjusted by preparing the type or themixture composition of the immersion solution (F) 14.

In order to obtain the thin and even antistatic film 9, the solution (F)14 is prepared so that the fine particles are absorbed onto the surfaceof the substrate 5 by a Van der Waals attraction between the surface ofthe substrate 5 and the fine particles and Coulomb repulsion between thesame signs of the fine particles causes the re-dispersion. Therefore, inthe fine particles which are temporarily absorbed and aggregated ontothe surface of the substrate 5, the re-dispersion occurs from the fineparticles which is located far away from the surface of the substrate 5and has the weak Van der Waals attraction, and a probability that thefine particles located near the surface of the substrate 5 continues tobe absorbed to the surface of the substrate 5 is increased.Consequently, according to difference in distance between the fineparticle and the surface of the substrate 5, the evenness of thethickness is achieved in the fine particle aggregation film 8.

The process of immersing the substrate 5 in the fine particle dispersionsolution (F) 14 and the aggregation solution (E) 13 after immersing thesubstrate 5 in the solution (F) 14 is repeated until the fine particleaggregation film 8 having the predetermined thickness is obtained.Finally the antistatic film 9 is obtained by performing the heattreatment similar to the first embodiment after drying to fix the fineparticle aggregation film 8 to the substrate 5.

Third Embodiment

FIGS. 6A, 6B, 6C, 6D, and 6E schematically show the process of a fifthembodiment. In FIGS. 6A, 6B, 6C, 6D, and 6E, the numeral 15 designates asolvent (a), and the same member as FIGS. 2A, 2B, 2C, 2D and 2E isdesignated by the same reference numeral.

Similarly to the first and second embodiments described above, the fifthembodiment is the technique of forming the fine particle aggregationfilm 8 without taking out the substrate 5 in a gas phase when thesubstrate 5 is alternately immersed in the different solutions.

The solvent (a) used in this embodiment is not compatible with the fineparticle dispersion solution (2) and the fine particle dispersionsolution (2) is the water solution as described above, so that theorganic solvent which is not compatible with the water is used as thesolvent (a). Specifically, alcohols which are not compatible with thewater, e.g. butanol is preferably used.

In the fifth embodiment, similarly to the first embodiment, the fineparticle dispersion solution 11 is prepared by mixing the adjustingsolution (C) 3 into the fine particle solution (A) 1 (see FIG. 6A). Atthis point, the mixture ratio or the composition of the fine particlesolution (A) and adjusting solution (C) are prepared so that the fineparticle aggregation does not occur in the fine particle dispersionsolution 11.

Then, the solvent (a) 15 is quietly poured into the fine particledispersion solution (2) 11 to prepare a treatment solution which isvertically separated into two solutions (FIG. 6B).

The substrate 5 is immersed in the phase of the fine particle dispersionsolution (2) 11 in the treatment solution and oscillated for severalseconds to several minutes, and the surface of the substrate 5 issufficiently wetted with the fine particle dispersion solution (2) 11(see FIG. 6C).

Then, the substrate 5 is pulled up to the phase of the solvent (a) (FIG.6D). By the operation, the large amount of solvent (a) 15 is substitutedfor the small amount of fine particle dispersion solution 11 wetting thesurface of the substrate 5 to instantly eliminate the dispersionstability of the fine particles. Therefore, the considerable amount offine particle is aggregated to the surface of the substrate 5 to formthe fine particle aggregation film 8 on the surface of the substrate 5.

In this embodiment, because the mixture of the solutions is limited tothe extremely small amount of solution which is moved by adhering to thesurface of the substrate 5, the functions of the fine particledispersion solution 11 and the solvent (a) 15 are maintained. Therefore,it is not necessary to newly prepare the fine particle dispersionsolution 11 and the solvent (a) 11, and it is possible to reciprocatethe substrate 5 between the two liquid phases using the same fineparticle dispersion solution 11 and the same solvent (a) 15. The fineparticle aggregation film 8 is deposited to the predetermined thicknessby repeating the reciprocating cycle, and then the antistatic film 9 isobtained by performing the heat treatment in the same way as the firstembodiment (FIG. 6E).

According to this embodiment, it is possible to reciprocate thesubstrate 5 between the two liquid phases without taking out thesubstrate 5 in air. Therefore, the fine particle aggregation film canmore efficiently be deposited on the substrate.

Fourth Embodiment

FIGS. 7A, 7B and 7C schematically show the process of a sixthembodiment. In FIGS. 7A, 7B and 7C, the numeral 21 designates a silanecoupling agent, the numeral 22 designates an exposure portion, thenumeral 23 designates a mask, the numeral 24 designates etchingtreatment, and the same member as FIGS. 1A to 1D is designated by thesame reference numeral.

The inventor found that the fine particles are hardly deposited onto thesurface of the substrate 5 when the surface of the substrate 5 ispreviously treated with the silane coupling agent. This embodiment isthe technique in which the fine particle aggregation film is preventedfrom depositing on a part of the surface of the substrate 5 toselectively form the antistatic film on other parts by utilizing thecharacteristics to perform the treatment of hydrophobic groupsubstitution to the part of the surface of the substrate 5.

First the outermost surface molecules of the substrate 5 are ended withthe hydrophobic group such as a methyl group by placing substrate 5 inan atmosphere of the silane coupling agent 21 (see FIG. 7A). Even if thefine particles are deposited on the substrate 5 treated as shown in FIG.9A by the process described in the first to third embodiments, thesurface of the substrate 5 is in the state in which the fine particleaggregation film 8 can not be deposited.

Any silane coupling agent, in which terminal functional group which isnot coupled to the substrate atom when the silane coupling agent iscoupled to the substrate 5 becomes the hydrophobic group, can be used inthe invention. For example, dimethyldiethoxysilane is preferably used.

In the substrate 5 whose whole surfaces are treated with the silanecoupling agent, only the part (selection portion 22) where the fineparticle aggregation film 8 is formed is exposed and other parts areshielded with the mask 23. In the state of things, only the hydrophobicgroups on the surface of the substrate 5 are removed by performing theetching treatment 24 (see FIG. 7B). The dry etching techniques such asUV radiation, UV ozone etching, and atmospheric plasma treatment aredesirably adopted as the etching treatment technique. However, it ispossible to adopt the wet etching technique, and it is possible to adoptmechanical polishing.

When the process of depositing the fine particle aggregation film likethe first to fifth embodiments is performed to the substrate 5 to whichthe etching treatment has been performed, the fine particle aggregationfilm is formed only in the selection portion 22 to which the etchingtreatment is performed and the fine particle aggregation film is notformed in other areas, so that the antistatic film 9 can selectively beformed (see FIG. 7C).

Alcohol is preferably used as the water-soluble organic solvent used inthe solutions (B), (E) and (F) in the first to fourth embodiments.Specifically, methyl alcohol, isopropyl alcohol (IPA), n-propanol, orthe like is solely used or at least the two alcohols described above areused according to the characteristics required for each solution used ineach embodiment. Ethers such as dioxane, amines such as monoethylamine,glycol ethers such as methyl Cellosolve, ketones such as acetone,carboxylic acids such as acetic acid, and esters such as Carbitolacetate can be used as the water-soluble organic solvent by appropriateselection in addition to alcohols.

Fifth Embodiment

The film depositing method of the invention is preferably applied to theformation of the antistatic film on the surface of a withstandingatmospheric pressure support body (spacer) in the plane type of imagedisplay device. FIG. 8 schematically shows a configuration of the imagedisplay device. In FIG. 10, the numeral 31 designates a front surfaceplate, the numeral 32 designates a rear surface plate, the numeral 33designates an outer peripheral frame, and the numeral 34 designates asupport body.

The front surface plate 31 is a glass plate in which a metal back or thelike is arranged, and high voltage ranging from 1 to 10 kV is applied tothe front surface plate 31. The rear surface plate 32 is a glasssubstrate in which a multiplicity of surface conductive type ofelectron-emission elements is arranged. The front surface plate 31 andthe rear surface plate 32 are bonded through the outer peripheral frame33, and the inside is held in vacuum. Therefore, the withstandingatmospheric pressure support body 34 is required in order to support theatmospheric pressure applied to the front surface plate 31 and the rearsurface plate 32. In order to withstand the high voltage and not toaccumulate electric charges on the surface by electron collision, theglass substrate in which the micro depressions and projections areformed on the surface is used as the support body 34 and the antistaticfilm is formed over the surface.

In the method of depositing the antistatic film of the invention, evenif a depth ranges from about 5 μm to about 20 μm and a width ranges fromabout 20 μm to about 40 μm in the micro depression portion or theprojection portion, the antistatic film can be formed with even filmthickness. The image display device to which the film depositing methodof the invention is applied is similar to Japanese Patent Laid-Open No.2003-223858 (US-2003-0141803A), so that the description will beneglected.

EXAMPLE 1

The antistatic film was formed by the process of the first embodimentwhile conditions were varied. Table 1 shows the result. In Table 1, IPSrepresents isopropyl alcohol, TMAH represents tetramethyl ammoniumhydroxide water solution, ATO represents antimony-doped (10mass-percent) tin oxide fine particles, and PD200 represents high strainpoint glass. The numeric value of substrate shape in Table 1 representsan interval between depressions.

In this embodiment, it was not perceived that the film is not formed onthe substrate surface on the condition 3-1 in which 100 mass % alcoholwas used as the aggregation solution (E). On the other conditions 3-1 to3-4, it was found that the thickness of the antistatic film can becontrolled according to the number of carbons in alcohol of theaggregation solution (E). Particularly, when n-propyl alcohol was usedas the solution (E) as shown in the condition 3-4, it was found that theantistatic film having the thickness of 1 μm can be formed in a time asshort as seven minutes and 30 minutes at five cycles. TABLE 1 3-1 3-23-3 3-4 Solution (A) 190 ml 190 ml 190 ml 190 ml Fine particle ATO 1 ATO1 ATO 1 ATO 1 material Water 99 Water 99 Water 99 Water 99 Mass part %Mass part % Mass part % Mass part % Solution (B) 230 ml 230 ml 230 ml230 ml Ethanol 100 Ethanol 100 Ethanol 100 Ethanol 100 Mass % Mass %Mass % Mass % Solution (C) 6 ml 6 ml 6 ml 6 ml TMAH 2 TMAH 2 TMAH 2 TMAH2 Water 98 Water 98 Water 98 Water 98 Mass % Mass % Mass % Mass %Solution (E) Methyl alcohol Ethanol 100 IPA 100 n-propanol 100 100 Mass% Mass % Mass % Mass % Fine particle 60 seconds 60 seconds 60 seconds 60seconds dispersion solution (1) Immersion time Solution (E) 30 seconds30 seconds 30 seconds 30 seconds Immersion time The number of Five timesFive times Five times Five times repetitions Solution heating NothingNothing Nothing Nothing Substrate Material PD200 PD200 PD200 PD200 ShapeForming with 30- Forming with 30- Forming with 30- Forming with 30- μmdepressions μm depressions μm depressions μm depressions and projectionsand projections and projections and projections Heat treatment 400° C.400° C. 400° C. 400° C. temperature Status of Film is not Even film ⊚Even film ⊚ Even film ⊚ deposited film deposited × Maximum film — 60 nm640 nm 1.2 μm thickness Average film — 50 nm 600 nm 1.0 μm thicknessSheet — 5 × 10⁹ Ω/□ 7 × 10⁷ Ω/□ 1 × 10⁶ Ω/□ resistance

The antistatic film was formed by the process of the second embodimentwhile conditions were varied. Table 2 shows the result. In the fourthembodiment, when ethanol in which the umber of carbons is small and thepolarity is large is used as the main component of the solution (F), thefine particle aggregation film formed once is substantially removed, andthe fine particle aggregation film can remain in the form of thecontinuous film. Therefore, the even and thin antistatic film could beobtained by adjusting the types and the composition ratio of thesolutions as shown in conditions 4-2 to 4-4. TABLE 2 4-1 4-2 4-3 4-4Solution (A) 190 ml 190 ml 190 ml 190 ml Fine particle ATO 1 ATO 1 ATO 1ATO 1 material Water 99 Water 99 Water 99 Water 99 Mass part % Mass part% Mass part % Mass part % Solution (B) 230 ml 230 ml 230 ml 230 mlEthanol 100 Ethanol 100 Ethanol 100 Ethanol 100 Mass % Mass % Mass %Mass % Solution (C) 6 ml 6 ml 6 ml 6 ml TMAH 2 TMAH 2 TMAH 2 TMAH 2Water 98 Water 98 Water 98 Water 98 Mass % Mass % Mass % Mass % Solution(E) Ethanol 70 Ethanol 70 Ethanol 70 Ethanol 70 IPA 30 IPA 30 IPA 30 IPA30 Mass % Mass % Mass % Mass % Solution (F) Methyl alcohol Methylalcohol Methyl alcohol Ethanol 100 100 70 20 Mass % Mass % IPA 300 IPA80 Mass % Mass % Fine particle 60 seconds 60 seconds 60 seconds 60seconds dispersion solution (1) Immersion time Solution (E) 30 seconds30 seconds 30 seconds 30 seconds Immersion time Solution (F) 30 seconds30 seconds 30 seconds 30 seconds Immersion time The number of Threetimes Three times Three times Three times repetitions Solution heatingNothing Nothing Nothing Nothing Substrate Material Quartz glass Quartzglass Quartz glass Quartz glass Shape Forming 50-μm Forming 50-μmForming 50-μm Forming 50-μm groove groove groove groove Heat treatment430° C. 430° C. 430° C. 430° C. temperature Status of Film is notStriped pattern Even film ◯ Even film ◯ deposited film deposited × filmΔ Maximum film — 20 nm 50 nm 65 μm thickness Average film — 10 nm 40 nm50 μm thickness Sheet — 2 × 10¹² Ω/□ 3 × 10¹⁰ Ω/□ 5 × 10⁹ Ω/□ resistance

The atmospheric pressure-resistant support body of the plane type ofimage display device is formed by the high strain point glass (PD200).The antistatic film was formed by performing the alternating immersionat three cycles on the condition 2-3 of the second embodiment to thesubstrate having a length of 600 mm, a height of 2 mm, and the thicknessof 1.8 mm, in which the depressions and projections having the depth of10 μm at periods of 35 μm were formed on the surface. As a result, theantistatic film having the sheet resistance of about 1×10¹⁰ Ω/cm² andthe thickness of 200 mm could evenly be formed on the whole surfacehaving the depressions and projections.

The image display device of the invention can be applied to thetelevision set. The television set to which the image display device ofthe invention is applied will be described below.

FIG. 10 is a block diagram of a television device according to theinvention. A receiving circuit C20 which includes a tuner and a decoderreceives television signals of a satellite broadcast, a ground wave, andthe like or data broadcast through a network, and the receiving circuitC20 outputs the decoded image data to an interface unit C30. Theinterface unit C30 converts the image data into a display format of animage display device C10 to output image data to the image displaydevice C10. The image display device C10 includes a display panel C11, adrive circuit C12, and a control circuit C13. The image display deviceshown in FIG. 8 can be applied to the image display device C10. Thecontrol circuit C13 outputs the image data and various control signalsto the drive circuit C12 while performing image processing such ascorrection processings suitable the display panel C11 to the input imagedata. The correction processings include a processing for retraining thevariation in brightness between picture elements in the vicinity of anatmospheric pressure-resistant support body (spacer) and pictureelements far from the atmospheric pressure-resistant support body(spacer), and it is preferable that the control circuit includes C13 hasa circuit for correcting brightness. The drive circuit C12 operates tooutput a driving signal to the display panel C11 on the basis ofinputted image data to display a television picture.

It is possible that the receiving circuit and the interface unit areaccommodated in an enclosure different from the image display device inthe form of a set-top box (STB), or it is possible that the receivingcircuit and the interface unit are accommodated in the same enclosure.

Since the film depositing method of the invention is not affected bysurface tension, and the antistatic film having the even thickness canbe formed on the substrate surface having the micro depressions andprojections. Since the film depositing method of the invention includesthe simple method of immersing the substrate in the solution, thecomplicated and expensive apparatus is not required, and the filmdepositing method of the invention can respond easily to upsizing of thesubstrate and mass production. Further, in the film deposition method ofthe invention, the solution used in the process is high in theutilization ratio, and the antistatic film can efficiently be formed athigh film deposition speed.

According to the invention, the antistatic film having the eventhickness can be formed on the surface of the member having the microdepressions and projections, such as the surface of the withstandingatmospheric pressure support body, in the plane type of image displaydevice, so that cost reduction can be achieved in the production whilereliability of the device can be improved.

This application claims priority from Japanese Patent Applications No.2003-432499 filed Dec. 26, 2003 and No. 2004-335386 filed Nov. 19, 2004,which are hereby incorporated by reference herein.

1. A method of forming a resistance film on a surface of a substratehaving an insulating surface, the resistance film having a sheetresistivity less than that of the insulating surface, the methodcomprising the steps of: immersing the substrate in a solution in whichfine particles made of a material of the resistance film are dispersedto wet a fine particle dispersion solution to the surface of thesubstrate; decreasing an absolute value of a ξ potential at the fineparticles in the fine particle dispersion solution wetted to the surfaceof the substrate so as to make it smaller than an absolute value of ξpotential at the fine particles when these particles are being dispersedin the solution, to deposit a fine particle aggregation film on thesurface of the substrate; and burning the fine particle aggregation filmto form the resistance film.
 2. The method of forming the resistancefilm according to claim 1, wherein in the depositing step the absolutevalue of the ξ potential at the fine particles in the fine particledispersion solution wetted to the surface of the substrate is set in therange of 0 to 40 mV.
 3. The method of forming the resistance filmaccording to claim 1, wherein the solution in which the fine particlesmade of the resistance film material are dispersed is a solutionobtained by adding a diluting solution having a polarity smaller thanthat of water and a dielectric constant lower than that of the water andan adjusting solution reducing the dispersion stability of the fineparticles into an aqueous solution in which the fine particles made ofthe resistance film material are dispersed.
 4. The method of forming theresistance film according to claim 3, wherein the depositing stepincludes a step of adding an aggregation solution having a polaritysmaller than that of the water and the dielectric constant lower thanthat of the water into the solution wetted to the surface of thesubstrate, the fine particles being dispersed in the solution.
 5. Themethod of forming the resistance film according to claim 4, wherein thepolarity of the aggregation solution is equal to or smaller than that ofthe diluting solution.
 6. The method of forming the resistance filmaccording to claim 3, wherein the depositing step includes a step ofimmersing the substrate immersed in the solution in which the fineparticles are disposed into an aggregation solution having a polaritysmaller than that of the water and a dielectric constant lower than thatof the water.
 7. The method of forming the resistance film according toclaim 6, wherein the polarity of the aggregation solution is equal to orsmaller than that of the diluting solution.
 8. The method of forming theresistance film according to claim 6, wherein a cycle of the wettingstep and the depositing step is repeated plural times.
 9. The method offorming the resistance film according to claim 3, wherein the dilutingsolution or the aggregation solution is alcohol.
 10. The method offorming the resistance film according to claim 3, wherein the adjustingsolution is an aqueous solution of quater ammonium.
 11. The method offorming the resistance film according to claim 3, wherein the adjustingsolution is an aqueous solution of tetramethyl ammonium hydroxide. 12.The method of forming the resistance film according to claim 9, whereinthe diluting solution or the aggregation solution is a solution ofethanol, IPA, methyl alcohol or n-propanol.
 13. The method of formingthe resistance film according to claim 8, further comprising a step ofimmersing the substrate into a re-dispersion solution after thedepositing step, the re-dispersion solution having a polarity largerthan that of the aggregation solution.
 14. The method of forming theresistance film according to claim 1, wherein a treatment solution inwhich two liquid phases are vertically separated is prepared by pouringan organic solvent which is not compatible as a whole with the fineparticle dispersion solution and forms a separate boundary into acontainer which stores the fine particle dispersion solution obtained bymixing an aqueous solution in which the fine particles made of anresistance film material are dispersed and an adjusting solutionreducing the dispersion stability of the fine particles, and the fineparticle aggregation film is deposited on the surface of the substrateby immersing the substrate into the treatment solution to reciprocatethe substrate between the fine particle dispersion solution phase andthe organic solvent phase.
 15. The method of forming the resistance filmaccording to claim 1, wherein a treatment by hydrophobic groupsubstitution is performed to a part of the surface of the substrate toprevent the fine particle aggregation film form depositing the part, sothat the resistance film is selectively formed in only parts where thetreatment by hydrophobic group substitution is not performed.
 16. Themethod of forming the resistance film according to claim 15, wherein thetreatment by hydrophobic group substitution performed to the substrateis a treatment performed with a silane coupling agent.
 17. The method offorming the resistance film according to claim 1, wherein the resistancefilm material mainly contains one of tin oxide, zinc oxide, titaniumoxide, and silicon oxide.
 18. The method of forming the resistance filmaccording to claim 2, wherein a diameter of the fine particle rangesfrom 4 to 20 nm in the solution in which the fine particles made of theresistance film material are dispersed.
 19. The method of forming theresistance film according to claim 1, wherein the substrate includes Sion its surface.
 20. The method of forming the resistance film accordingto claim 1, wherein the surface of the substrate has 10 to 100 μmdepressions and projections.
 21. An image display device comprising: arear plate which has electron-emission elements; a front plate which hasan image display member; and an atmospheric pressure-resistant supportbody which is located between the rear plate and the front plate,wherein the atmospheric pressure-resistant support body has a substrateand an resistance film with which the substrate is covered, and theresistance film is formed by the method according to claim
 1. 22. Atelevision device comprising: the image display device according toclaim 21; a television signal receiving circuit; and an interface unitwhich connects the image display device and the television signalreceiving circuit.
 23. The television device according to claim 22, theimage display device have a circuit unit for restraining the variationin brightness due to the atmospheric pressure-resistant support body,wherein the circuit unit serves to correct the image signal from theinterface unit.